The present invention relates to a fuel injection device for supplying fuel to the cylinders of an internal combustion engine, and more particularly to a fuel injection device having a pressurization chamber for pressurizing introduced fuel and a fuel chamber, the pressurization and fuel chambers being held in communication with each other by a solenoid valve which is selectively openable and closable for controlling fuel injection.
There is known a fuel injection device associated with an internal combustion engine, the fuel injection device having a pressurization chamber for pressurizing introduced fuel, a fuel chamber, and a solenoid valve by which the pressurization and fuel chambers are held in communication with each other, the solenoid valve being selectively openable and closable under the control of a signal indicative of operating conditions of the engine. This known fuel injection device controls the quantity of fuel to be injection and the timing of fuel injection without using a mechanism for controlling the quantity of fuel to be injection and a mechanism for controlling the timing of fuel injection (so-called "timer"). Various detected signals representative of the rotational speed of the drive shaft of a fuel injection pump, the temperature in the fuel chamber, the pressure in an intake pipe of the engine, the quantity of depression of the accelerator pedal, and the position of the top dead center of each cylinder are supplied to an electronic control unit which then calculates the timing of fuel injection and the quantity of fuel to be injected according to operating conditions of the engine for controlling the opening and closing of the solenoid valve.
The fuel injection control effected by a solenoid-valve-controlled fuel injection device is dependent on the timing at which the solenoid valve is opened and closed. Therefore, the valve opening/closing timing must accurately be controlled. With the aforesaid conventional fuel injection device, however, no special consideration is given to delay times that are present in opening and closing the solenoid valve. As a result, the timing of fuel injection and the quantity of fuel to be injected cannot be controlled to a nicety by the prior fuel injection device.
In order to eliminate the above drawback, it has been proposed to correct the duration (Tv) of a control pulse for driving a solenoid valve with a valve closing delay time (Tsdv) and a valve opening delay time (Tedv) and to apply a pulse having a duration (Dp=Tsdv+Tv-Tedv) as a valve driving pulse to actuate the solenoid valve for thereby obtaining a desired timing of fuel injection and a desired quantity of fuel to be injected.
The above proposed arrangement with the pulse duration correction is advantageous in that the period in which the solenoid valve is open is controlled by supplying the solenoid valve with a pulse having a pulse duration corrected in view of the valve closing delay time and the valve opening delay time.
The valve closing delay timd and the valve opening delay time are detected for each valve opening/closing cycle by respective measuring means. The solenoid valve is regarded as starting to be opened and closed when an inner valve and a valve casing of the solenoid valve are brought into and out of contact with each other. Thus, the solenoid valve itself serves as contacts. When the solenoid valve is opened, the inner valve bounces and hence the contacts are repeatedly turned on and off.
At times, a command for opening the solenoid valve is applied while the inner valve is bouncing. This phenomenon is more likely to happen as the rotational speed of the engine goes higher. As a consequence, the valve opening delay time cannot be measured precisely. The duration of a valve driving pulse computed using the inaccurately measured valve opening delay time is therefore inaccurate and so is the controlling of the quantity of fuel to be injected.
If a pre-measured valve opening delay time is used a fixed valve opening delay time, it would be impossible to correct the duration of a valve driving pulse as a function of a time-dependent change in the valve opening delay time.
On the other hand, if the valve opening delay time measured in a preceding valve control cycle is used in a present valve control cycle, the durations of valve driving pulses are subject to a relatively large variation as the degree of valve opening varies gradually when a valve opneing signal is issued. Consequently, the quantity of fuel to be injected cannot be controlled precisely.